Managing transmit power for better frequency re-use in TV white space

ABSTRACT

Certain aspects of the present disclosure provide techniques and apparatus for managing transmit power in a television white space (TVWS) network. One example method generally includes transmitting a sequence of request-to-send (RTS) messages at different transmit power levels to an apparatus and determining if a clear-to-send (CTS) message was received in response to at least one of the RTS messages corresponding to a particular one of the transmit power levels. Another example method generally includes receiving, at a first apparatus from a second apparatus, a packet that cannot be decoded by the first apparatus; determining at least one of a time or a duration corresponding to the packet; transmitting a query with an indication of the at least one of the time or the duration; and receiving a message from the second apparatus in response to the query, the message identifying the second apparatus as a source of the packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/397,450 (Atty. Dkt. No. 111024U1), filed Feb. 15, 2012, which claimsbenefit of U.S. Provisional Patent Application Ser. No. 61/443,587(Atty. Dkt. No. 111024P1), filed Feb. 16, 2011, which is hereinincorporated by reference.

BACKGROUND

Field of the Invention

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to managing transmit power in atelevision white space (TVWS) network.

Relevant Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communications systems, different schemes arebeing developed. One scheme known as “white-fi” entails expanding Wi-Fitechnology with the unused frequency spectrum in the television (TV)band (i.e., the TV white space). An Institute of Electrical andElectronics Engineers (IEEE) 802.11af task group has been created todefine an amendment to the IEEE 802.11 standard for using the TV whitespace (TVWS). The IEEE 802.11 denotes a set of Wireless Local AreaNetwork (WLAN) air interface standards developed by the IEEE 802.11committee for short-range communications (e.g., tens of meters to a fewhundred meters). However, by using the TVWS with frequencies below 1GHz, IEEE 802.11af may offer greater propagation distances to beachieved, in addition to the increased bandwidth offered by the unusedfrequencies in the TV spectrum.

SUMMARY

Certain aspects of the present disclosure generally relate to managingtransmit power in a television white space (TVWS) network. By managingtransmit power as described herein, medium re-use may be improved insuch a network, and unfair usage problems may be alleviated.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes atransmitter configured to transmit a sequence of request-to-send (RTS)messages at different transmit power levels to a second apparatus and aprocessing system configured to determine if a clear-to-send (CTS)message was received in response to at least one of the RTS messagescorresponding to a particular one of the transmit power levels.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes transmitting a sequence ofRTS messages at different transmit power levels to an apparatus anddetermining if a CTS message was received in response to at least one ofthe RTS messages corresponding to a particular one of the transmit powerlevels.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes meansfor transmitting a sequence of RTS messages at different transmit powerlevels to a second apparatus and means for determining if a CTS messagewas received in response to at least one of the RTS messagescorresponding to a particular one of the transmit power levels.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to transmit a sequence of RTS messages at different transmitpower levels to an apparatus and to determine if a CTS message wasreceived in response to at least one of the RTS messages correspondingto a particular one of the transmit power levels.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a transmitterconfigured to transmit, via the at least one antenna, a sequence of RTSmessages at different transmit power levels to an apparatus; and aprocessing system configured to determine if a CTS message was receivedin response to at least one of the RTS messages corresponding to aparticular one of the transmit power levels.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes areceiver configured to receive from a second apparatus a packet thatcannot be decoded by the first apparatus; a processing system configuredto determine at least one of a time or a duration corresponding to thepacket; and a transmitter configured to transmit a query with anindication of the at least one of the time or the duration, wherein thereceiver is configured to receive a message from the second apparatus inresponse to the query, the message identifying the second apparatus as asource of the packet.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving, at a firstapparatus from a second apparatus, a packet that cannot be decoded bythe first apparatus; determining at least one of a time or a durationcorresponding to the packet; transmitting a query with an indication ofthe at least one of the time or the duration; and receiving a messagefrom the second apparatus in response to the query, the messageidentifying the second apparatus as a source of the packet.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes meansfor receiving from a second apparatus a packet that cannot be decoded bythe first apparatus; means for determining at least one of a time or aduration corresponding to the packet; and means for transmitting a querywith an indication of the at least one of the time or the duration,wherein the means for receiving is configured to receive a message fromthe second apparatus in response to the query, the message identifyingthe second apparatus as a source of the packet.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to receive, at a first apparatus from a second apparatus, apacket that cannot be decoded by the first apparatus; to determine atleast one of a time or a duration corresponding to the packet; totransmit a query with an indication of the at least one of the time orthe duration; and to receive a message from the second apparatus inresponse to the query, the message identifying the second apparatus as asource of the packet.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a receiverconfigured to receive, from an apparatus via the at least one antenna, apacket that cannot be decoded by the wireless node; a processing systemconfigured to determine at least one of a time or a durationcorresponding to the packet; and a transmitter configured to transmit,via the at least one antenna, a query with an indication of the at leastone of the time or the duration, wherein the receiver is configured toreceive a message from the apparatus in response to the query, themessage identifying the apparatus as a source of the packet.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes atransmitter configured to transmit a packet at a particular time with acertain duration, a receiver configured to receive from a secondapparatus a query with an indication of at least one of a query time ora query duration for the packet, and a processing system. The processingsystem is typically configured to store at least one of the particulartime or the certain duration for the packet and to determine that the atleast one of the query time or the query duration substantially matchesthe at least one of the stored time or the stored duration, wherein thetransmitter is configured to transmit a message to the second apparatusin response to the query, the message identifying the first apparatus asa source of the packet.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes transmitting, at a firstapparatus, a packet at a particular time with a certain duration;storing at least one of the particular time or the certain duration forthe packet; receiving from a second apparatus a query with an indicationof at least one of a query time or a query duration for the packet;determining that the at least one of the query time or the queryduration substantially matches the at least one of the stored time orthe stored duration; and transmitting a message to the second apparatusin response to the query, the message identifying the first apparatus asa source of the packet.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes meansfor transmitting a packet at a particular time with a certain duration;means for storing at least one of the particular time or the certainduration for the packet; means for receiving from a second apparatus aquery with an indication of at least one of a query time or a queryduration for the packet; and means for determining that the at least oneof the query time or the query duration substantially matches the atleast one of the stored time or the stored duration, wherein the meansfor transmitting is configured to transmit a message to the secondapparatus in response to the query, the message identifying the firstapparatus as a source of the packet.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to transmit from a first apparatus a packet at a particulartime with a certain duration; to store at least one of the particulartime or the certain duration for the packet; to receive from a secondapparatus a query with an indication of at least one of a query time ora query duration for the packet; to determine that the at least one ofthe query time or the query duration substantially matches the at leastone of the stored time or the stored duration; and to transmit a messageto the second apparatus in response to the query, the messageidentifying the first apparatus as a source of the packet.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a transmitterconfigured to transmit, via the at least one antenna, a packet at aparticular time with a certain duration; a receiver configured toreceive, from an apparatus via the at least one antenna, a query with anindication of at least one of a query time or a query duration for thepacket; and a processing system. The processing system is typicallyconfigured to store at least one of the particular time or the certainduration for the packet and to determine that the at least one of thequery time or the query duration substantially matches the at least oneof the stored time or the stored duration, wherein the transmitter isconfigured to transmit a message to the apparatus in response to thequery, the message identifying the wireless node as a source of thepacket.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a processingsystem configured to determine a highest transmit power for transmittingdata frames from the apparatus and a transmitter configured to transmita message with an indication of the highest transmit power.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes determining a highesttransmit power for transmitting data frames and transmitting a messagewith an indication of the highest transmit power.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a highest transmit power for transmitting data frames fromthe apparatus and means for transmitting a message with an indication ofthe highest transmit power.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to determine a highest transmit power for transmitting dataframes from an apparatus and to transmit a message from the apparatuswith an indication of the highest transmit power.

Certain aspects of the present disclosure provide an access point (AP).The AP generally includes at least one antenna, a processing systemconfigured to determine a highest transmit power for transmitting dataframes from the access point, and a transmitter configured to transmit,via the at least one antenna, a message with an indication of thehighest transmit power.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes areceiver configured to receive, from a second apparatus, a message withan indication of a highest transmit power used by the second apparatusfor transmitting data frames; and a processing system configured todetermine that the second apparatus is a dominant interferer based, atleast in part, on the highest transmit power.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving, from anapparatus, a message with an indication of a highest transmit power usedby the apparatus for transmitting data frames; and determining that theapparatus is a dominant interferer based, at least in part, on thehighest transmit power.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes meansfor receiving, from a second apparatus, a message with an indication ofa highest transmit power used by the second apparatus for transmittingdata frames; and means for determining that the second apparatus is adominant interferer based, at least in part, on the highest transmitpower.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to receive, from an apparatus, a message with an indicationof a highest transmit power used by the apparatus for transmitting dataframes; and to determine that the apparatus is a dominant interfererbased, at least in part, on the highest transmit power.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a receiverconfigured to receive, from an apparatus via the at least one antenna, amessage with an indication of a highest transmit power used by theapparatus for transmitting data frames; and a processing systemconfigured to determine that the apparatus is a dominant interfererbased, at least in part, on the highest transmit power.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a processingsystem configured to determine a first transmit power for transmittingdata frames from the apparatus and a transmitter configured to transmita control or management message at a second transmit power, wherein thecontrol or management message comprises a first indication of the firsttransmit power and a second indication of the second transmit power.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes determining a firsttransmit power for transmitting data frames and transmitting a controlor management message at a second transmit power, wherein the control ormanagement message comprises a first indication of the first transmitpower and a second indication of the second transmit power.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a first transmit power for transmitting data frames from theapparatus and means for transmitting a control or management message ata second transmit power, wherein the control or management messagecomprises a first indication of the first transmit power and a secondindication of the second transmit power.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to determine a first transmit power for transmitting dataframes from an apparatus and to transmit a control or management messageat a second transmit power, wherein the control or management messagecomprises a first indication of the first transmit power and a secondindication of the second transmit power.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a processingsystem configured to determine a first transmit power for transmittingdata frames from the wireless node; and a transmitter configured totransmit, via the at least one antenna, a control or management messageat a second transmit power, wherein the control or management messagecomprises a first indication of the first transmit power and a secondindication of the second transmit power.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes areceiver configured to receive, from a second apparatus, a control ormanagement message with a first indication of a first transmit powerused by the second apparatus for transmitting data frames; and aprocessing system configured to determine that the second apparatus is adominant interferer based, at least in part, on the first transmitpower.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving, from anapparatus, a control or management message with a first indication of afirst transmit power used by the apparatus for transmitting data framesand determining that the apparatus is a dominant interferer based, atleast in part, on the first transmit power.

Certain aspects of the present disclosure provide a first apparatus forwireless communications. The first apparatus generally includes meansfor receiving, from a second apparatus, a control or management messagewith a first indication of a first transmit power used by the secondapparatus for transmitting data frames; and means for determining thatthe second apparatus is a dominant interferer based, at least in part,on the first transmit power.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to receive, from an apparatus, a control or managementmessage with a first indication of a first transmit power used by theapparatus for transmitting data frames; and to determine that theapparatus is a dominant interferer based, at least in part, on the firsttransmit power.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a receiverconfigured to receive, from an apparatus via the at least one antenna, acontrol or management message with a first indication of a firsttransmit power used by the apparatus for transmitting data frames; and aprocessing system configured to determine that the apparatus is adominant interferer based, at least in part, on the first transmitpower.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a processingsystem configured to determine a modulation and coding scheme (MCS) fortransmitting data frames from the apparatus and a transmitter configuredto transmit a request message comprising an indication of the MCS.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes determining a modulationand coding scheme (MCS) for transmitting data frames and transmitting arequest message comprising an indication of the MCS.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a modulation and coding scheme (MCS) for transmitting dataframes from the apparatus and means for transmitting a request messagecomprising an indication of the MCS.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to determine a modulation and coding scheme (MCS) fortransmitting data frames from an apparatus; and to transmit a requestmessage comprising an indication of the MCS.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a processingsystem configured to determine a modulation and coding scheme (MCS) fortransmitting data frames from the wireless node; and a transmitterconfigured to transmit, via the at least one antenna, a request messagecomprising an indication of the MCS.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a receiverconfigured to receive a request message comprising an indication of amodulation and coding scheme (MCS) for transmitting data frames to bereceived; a processing system configured to determine a link marginbased on the MCS; and a transmitter configured to transmit a responsemessage with an indication of the link margin.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving a requestmessage comprising an indication of a modulation and coding scheme (MCS)for transmitting data frames to be received; determining a link marginbased on the MCS; and transmitting a response message with an indicationof the link margin.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving a request message comprising an indication of a modulation andcoding scheme (MCS) for transmitting data frames to be received; meansfor determining a link margin based on the MCS; and means fortransmitting a response message with an indication of the link margin.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium having instructionsexecutable to receive a request message comprising an indication of amodulation and coding scheme (MCS) for transmitting data frames to bereceived, to determine a link margin based on the MCS, and to transmit aresponse message with an indication of the link margin.

Certain aspects of the present disclosure provide a wireless node. Thewireless node generally includes at least one antenna; a receiverconfigured to receive, via the at least one antenna, a request messagecomprising an indication of a modulation and coding scheme (MCS) fortransmitting data frames to be received; a processing system configuredto determine a link margin based on the MCS; and a transmitterconfigured to transmit, via the at least one antenna, a response messagewith an indication of the link margin.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a diagram of a wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates a table of device modes for television white space(TVWS) as defined by the Federal Communications Commission (FCC), inaccordance with certain aspects of the present disclosure.

FIG. 5 illustrates different ranges at which a fixed device may bedetected and may detect portable devices, in accordance with certainaspects of the present disclosure.

FIG. 6 illustrates a transmit power control (TPC) report element inaccordance with certain aspects of the present disclosure.

FIG. 7 illustrates example operations to determine, from the perspectiveof a portable device, interfering fixed devices using a sequence ofmessages sent at different transmit power levels, in accordance withcertain aspects of the present disclosure.

FIG. 7A illustrates example components for performing the operationsshown in FIG. 7.

FIG. 8 illustrates an example hidden node problem in accordance withcertain aspects of the present disclosure.

FIG. 9 illustrates an example exposed node problem in accordance withcertain aspects of the present disclosure.

FIG. 10 illustrates a node causing interference and deferral to aneighboring node in accordance with certain aspects of the presentdisclosure.

FIG. 11 illustrates using a start time of a packet to forceidentification of an unknown node, in accordance with certain aspects ofthe present disclosure.

FIG. 12 illustrates example operations to learn, from the perspective ofa wireless node, the transmit power used by an unknown neighboring node,in accordance with certain aspects of the present disclosure.

FIG. 12A illustrates example components for performing the operationsshown in FIG. 12.

FIG. 13 illustrates example operations to provide, from the perspectiveof a wireless node unknown to a neighboring node, the transmit powerused by the wireless node, in accordance with certain aspects of thepresent disclosure.

FIG. 13A illustrates example components for performing the operationsshown in FIG. 13.

FIG. 14A illustrates a TPC request element and a TPC report element, inaccordance with certain aspects of the present disclosure.

FIG. 14B illustrates a TPC request element with a modulation and codingscheme (MCS) field and a TPC report element, in accordance with certainaspects of the present disclosure.

FIG. 15 illustrates example operations to utilize, from the perspectiveof a transmitter, a TPC request message with a desired MCS, inaccordance with certain aspects of the present disclosure.

FIG. 15A illustrates example components for performing the operationsshown in FIG. 15.

FIG. 16 illustrates example operations to utilize, from the perspectiveof a receiver, a TPC request message with a desired MCS, in accordancewith certain aspects of the present disclosure.

FIG. 16A illustrates example components for performing the operationsshown in FIG. 16.

FIG. 17 illustrates an example station (STA) surrounded by interferingSTAs, in accordance with certain aspects of the present disclosure.

FIG. 18 illustrates an example beacon information element (IE) forindicating the transmit power of data frames transmitted from an accesspoint (AP), in accordance with certain aspects of the presentdisclosure.

FIG. 19 illustrates example operations to transmit, from the perspectiveof an AP, a broadcast message with an indication of the highest transmitpower for transmitting data frames, in accordance with certain aspectsof the present disclosure.

FIG. 19A illustrates example components for performing the operationsshown in FIG. 19.

FIG. 20 illustrates example operations to determine, from theperspective of a STA, dominant interferers based on a received broadcastmessage with an indication of a highest transmit power for transmittingdata frames, in accordance with certain aspects of the presentdisclosure.

FIG. 20A illustrates example components for performing the operationsshown in FIG. 20.

FIG. 21 illustrates an example control or management frame format withan IE for indicating the transmit power of data frames transmitted froma STA and another IE for indicating the transmit power used fortransmitting the control or management frame, in accordance with certainaspects of the present disclosure.

FIG. 22 illustrates example operations to transmit, from the perspectiveof a STA, a control or management message with an indication of atransmit power for transmitting data frames and another indication of atransmit power used when transmitting the control or management message,in accordance with certain aspects of the present disclosure.

FIG. 22A illustrates example components for performing the operationsshown in FIG. 22.

FIG. 23 illustrates example operations to determine, from theperspective of a STA, dominant interferers based on a received controlor management message with an indication of a transmit power fortransmitting data frames and another indication of a transmit power usedwhen transmitting the control or management message, in accordance withcertain aspects of the present disclosure.

FIG. 23A illustrates example components for performing the operationsshown in FIG. 23.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to a different user terminal. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) totransmit on sub-carriers that are distributed across the systembandwidth, localized FDMA (LFDMA) to transmit on a block of adjacentsub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks ofadjacent sub-carriers. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNode B, Radio Network Controller (“RNC”), evolved Node B (eNB), BaseStation Controller (“BSC”), Base Transceiver Station (“BTS”), BaseStation (“BS”), Transceiver Function (“TF”), Radio Router, RadioTransceiver, Basic Service Set (“BSS”), Extended Service Set (“ESS”),Radio Base Station (“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known as asubscriber station, a subscriber unit, a mobile station (“MS”), a remotestation, a remote terminal, a user terminal (“UT”), a user agent, a userdevice, user equipment (“UE”), a user station, or some otherterminology. In some implementations, an access terminal may comprise acellular telephone, a cordless telephone, a Session Initiation Protocol(“SIP”) phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a tablet, a portable communicationdevice, a portable computing device (e.g., a personal data assistant),an entertainment device (e.g., a music or video device, or a satelliteradio), a global positioning system (GPS) device, or any other suitabledevice that is configured to communicate via a wireless or wired medium.In some aspects, the node is a wireless node. Such wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as the Internet or a cellular network) via a wired orwireless communication link.

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system 100 with access points and user terminals. For simplicity,only one access point 110 is shown in FIG. 1. An access point isgenerally a fixed station that communicates with the user terminals andmay also be referred to as a base station or some other terminology. Auser terminal may be fixed or mobile and may also be referred to as amobile station, a wireless device, or some other terminology. Accesspoint 110 may communicate with one or more user terminals 120 at anygiven moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal. A system controller130 couples to and provides coordination and control for the accesspoints.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects, anAP 110 may be configured to communicate with both SDMA and non-SDMA userterminals. This approach may conveniently allow older versions of userterminals (“legacy” stations) to remain deployed in an enterprise,extending their useful lifetime, while allowing newer SDMA userterminals to be introduced as deemed appropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsubbands with OFDM, and so on. Each selected user terminal transmitsuser-specific data to and/or receives user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same or different number of antennas.

The MIMO system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, each time slot beingassigned to different user terminal 120.

FIG. 2 illustrates a block diagram of access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 t. User terminal 120 m isequipped with N_(ut,m) antennas 252 ma through 252 mu, and user terminal120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu. Theaccess point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. Each user terminal 120 is atransmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, N_(dn) user terminals areselected for simultaneous transmission on the downlink, N_(up) may ormay not be equal to N_(dn), and N_(up) and N_(dn) may be static valuesor can change for each scheduling interval. The beam-steering or someother spatial processing technique may be used at the access point anduser terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic datafor the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 tothe access point.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals performs spatial processing onits data symbol stream and transmits its set of transmit symbol streamson the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal. TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing (such as a precoding or beamforming, as described in thepresent disclosure) on the N_(dn) downlink data symbol streams, andprovides N_(ap) transmit symbol streams for the N_(ap) antennas. Eachtransmitter unit 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222providing N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit 254 processesa received signal from an associated antenna 252 and provides a receivedsymbol stream. An RX spatial processor 260 performs receiver spatialprocessing on N_(ut,m) received symbol streams from N_(ut,m) receiverunits 254 and provides a recovered downlink data symbol stream for theuser terminal. The receiver spatial processing is performed inaccordance with the CCMI, MMSE or some other technique. An RX dataprocessor 270 processes (e.g., demodulates, deinterleaves and decodes)the recovered downlink data symbol stream to obtain decoded data for theuser terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). Controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point. Controllers 230 and 280also control the operation of various processing units at access point110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the MIMO system 100. The wirelessdevice 302 is an example of a device that may be configured to implementthe various methods described herein. The wireless device 302 may be anaccess point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

CSMA Operation in TVWS

As described above, IEEE 802.11af is an extension of the IEEE 802.11standard into the TV white space. As used herein, the term “white space”generally refers to unused frequencies in the electromagnetic spectrum,and the term “TV white space” generally refers to the unused frequencyspectrum in the TV band (e.g., the radio frequencies historicallyallocated for analog television, but now available due to the conversionto digital television). No physical (PHY)/MAC (media access control)layer changes are being considered in this extension. Several frameformats are added for the enablement procedure.

FIG. 4 illustrates a table 400 of device modes for television whitespace (TVWS) as defined by the Federal Communications Commission (FCC).TVWS devices include fixed devices, which may most likely be installedby a professional and have the locations of the individual devicesentered into a database. The maximum transmit power for fixed devices is36 dBm. Mobile/portable TVWS devices include Mode 1 and Mode 2 devices,whose locations are not registered. The maximum transmit power forportable devices is 20 dBm. Fixed and Mode 2 devices are termed enablingstations (STAs), while a device in a Mode 1 operational state is termeda dependent STA. Although transmit power control is not required in theIEEE 802.11 standard, the FCC recommends (or may even mandate) usingtransmit power control in the TVWS.

Once devices are enabled, the devices are expected to use Carrier SenseMultiple Access (CSMA) MAC for communication. However, a number ofproblems are expected when using CSMA in the TVWS. For example, largerpropagation range available with TVWS increases the likelihood of hiddennodes and increases the number of contending nodes. CSMA performance issensitive to the presence of hidden nodes and the number of contendingnodes. Another problem is diversity in transmit powers due to fixed andportable devices using different transmit powers and to the utilizationof transmit power control. Such diversity causes asymmetry in thecoverage areas of different transmitters, leading not only to theincreased possibility of hidden or exposed nodes, but also to increasedcollisions and unfair access.

Accordingly, what is needed are techniques and apparatus for improvedCSMA operation between fixed and portable devices in an effort to atleast alleviate, if not completely solve, these problems.

Transmit Power Management in TVWS

The difference in transmit power between fixed and portable devices issubstantial. The range of fixed devices is larger than that of portabledevices. For example, there is a 10 dBm link budget difference betweenthe range at which a portable device hears a fixed device and the rangeat which a fixed device hears a portable device.

FIG. 5 illustrates a fixed TVWS device 500, such as an access point (AP)110. The inner circle 502 represents a range at which the fixed device500 can detect portable devices, whereas the outer circle 504 representsthe range at which the fixed device 500 can be detected. The radius ofthe inner circle 502 is approximately half the radius of the outercircle 504. The area between the inner circle 502 and the outer circle504 represents a region 506 where the fixed device 500 does not defer toportable devices.

To allow for co-existence of fixed and portable devices, portabledevices may most likely use a channel that has a neighboring fixeddevice only if the fixed device is sufficiently close to hear theportable device. To determine interfering fixed devices, a reportelement the same as, or at least similar to, a transmit power control(TPC) report element in IEEE 802.11 may be used.

FIG. 6 illustrates a TPC report element 600, in accordance with certainaspects of the present disclosure. The TPC report element 600 maycomprise an element identification (ID) field 602, a length field 604, atransmit power field 606, and a link margin field 608. Each of thesefields 602-608 may have a length of one octet (8 bits).

For certain aspects, portable devices may implement a two-step procedureto determine interfering fixed devices. First, a portable device mayidentify high transmit power fixed devices by monitoring the TPC elementin the beacons received. Next, the portable device may send a proberequest with a wild card service set identifier (SSID) and a TPCrequest. This request may be sent at the lowest PHY rate. Response TPCelements from fixed devices may most likely contain the link marginbased on the TPC request. As used herein, the “link margin” generallyrefers to the difference between a wireless receiver's sensitivity andthe actual received power, typically measured in decibels (dB). Theportable device may use the link margin to determine transmit power toensure that transmissions from the portable devices are “heard” at fixeddevices. If several fixed devices do not respond to the TPC request, theportable device may assume that the portable device itself is “hidden”from such fixed devices and may move to another channel. This two-stepprocedure may entail a standards change to ensure that a TPC response toTPC requests with a wild card SSID is mandatory.

For certain aspects, an alternate procedure may be used to determineinterfering fixed devices, which need not entail a standards change. Inthis alternate procedure, a sequence of request-to-send (RTS) messagesmay be sent at increasing powers to each of the identified high transmitpower fixed devices, and the minimum power level involved for aclear-to-send (CTS) response may be determined. If several fixed devicesdo not respond to the RTS messages, even at the highest power, theportable device may most likely assume that the device itself is“hidden” from such fixed devices and move to another channel.

Because fixed devices may typically be designed to register theirlocation and utilized channel, a database may aid in the discovery offixed devices. Portable devices may most likely be capable of queryingfor the fixed devices in the vicinity of the portable devices. Forexample, a portable device may be able to obtain a list of fixed devicesin a 200 m radius from the portable device's location. A response fromthe database may include the locations, operating channels, and transmitpower levels of the fixed devices.

FIG. 7 illustrates example operations 700 to determine, from theperspective of a portable device, for example, interfering fixed devicesusing a sequence of messages sent at different transmit power levels, inaccordance with certain aspects of the present disclosure. Theoperations may begin, at 702, with the portable device transmitting asequence of request-to-send (RTS) messages at different power levels toan apparatus, such as a fixed TVWS device. For certain aspects, thesequence of RTS messages may comprise RTS messages transmitted withincreasing power. The portable device may transmit the sequence of RTSmessages via one or more channels in the TVWS.

At 704, the portable device may determine if a clear-to-send (CTS)message was received in response to at least one of the RTS messagescorresponding to a particular one of the transmit power levels. Forcertain aspects, the portable device may transmit at least one of data,a subsequent RTS message, or a subsequent CTS message at 706 to theapparatus, based on the particular one of the transmit power levels. Forcertain aspects, the particular one of the transmit power levels is aminimum transmit power level for transmitting one of the RTS messages tothe apparatus and for receiving the CTS message in response.

According to certain aspects, the portable device may identify theapparatus. The apparatus may identify the apparatus by sending a queryabout any fixed apparatuses nearby (i.e., in a vicinity of the portabledevice) and receiving a response to the query. The response may includeat least one of a location of the fixed apparatus, an operating channelfor the fixed apparatus, or a transmit power level of the fixedapparatus.

For certain aspects, the portable device may transmit the sequence ofRTS messages using a first channel. If the CTS message is not received,the portable device may transmit the sequence of RTS messages using asecond channel, different than the first channel.

When transmit devices use transmit power control, larger medium re-useand decreased contention may result if the range of individual transmitdevices is small. However, diversity in transmit powers may cause hiddennode problems with higher collision probability and/or unfair mediumaccess for devices that use lower power when neighboring devices usehigher power. Therefore, the transmit power used may most likely be highenough to ensure the highest possible modulation and coding scheme (MCS)is received. This may lead to carrier sense at potentially interferingneighbors.

FIG. 8 illustrates an example hidden node problem in accordance withcertain aspects of the present disclosure. In FIG. 8, node A transmitsat a lower power than node C. Node C does not defer to transmissions ofnode A, thereby causing collisions at node B. In order to solve thisproblem, packet-drop-based rate adaptation may involve a transmit powerincrease at the transmitter side. The transmit power may be increased toa level to force deferral at node C. If RTS/CTS is used, node B mayadjust the power of the CTS to ensure that node B's interferingneighbors are quiet as another solution to this problem at the receiverside. These solutions may also be combined. Methods for identifyinginterfering neighbors are described below.

FIG. 9 illustrates an example exposed node problem with transmit powercontrol in accordance with certain aspects of the present disclosure. Ifnode A has a lower transmit power than node C such that node A defers tonode C, but node C does not defer to node A, then medium access at nodeA would be lower than that at node C. If transmissions of node A arereceived at node B, then there are no collisions to trigger a powerincrease at node A. To ensure fair access, node A may most likely beable to determine if node A's lower access is due to a few nodes that donot defer to node A or due to a network with many nodes. This may entaila method to identify neighbors that cause deferral at node A, althoughdecoding of the transmissions to determine MAC addresses may not befeasible. If the neighbors can be identified, then node A may ramp upnode A's transmit power to force deferral at node A's neighbors.

FIG. 10 illustrates a node causing interference and deferral to aneighboring node in accordance with certain aspects of the presentdisclosure. In FIG. 10 transmissions from node B cause deferral at nodeA. In order to discover neighbors that cause interference and deferral,two different cases may be considered. In the first case, node A is ableto decode packets from node B. Therefore, node A may send a TPC requestto node B to determine the transmit power of node B. Node A may then usesufficient power to ensure deferral at node B.

In the second case, node A cannot decode packets from node B (e.g., dueto the MCS used). Accordingly, what is needed is a method for node A tobe able to determine its potential neighbors and then transmit at asuitable power level.

FIG. 11 illustrates using a start time of a packet 1100 having apreamble 1102 and a payload 1104 to force identification of an unknownnode, in accordance with certain aspects of the present disclosure. Inthis manner, neighbor discovery may be accomplished based on the packetstart time. When node A defers to a transmission from an unknown node,node A decodes the preamble 1102 and records the exact time at which thenode received the preamble. Node A then sends a query with a broadcastreceive address and the time stamp (relative to the transmit time of thepacket that caused deferral). For certain aspects, time stamps forseveral packets in the past may be included in an effort to discovermultiple neighbors.

STAs (such as node B) may receive the query check if the STAs hadtransmitted a packet at the time provided in the query message. If thetime stamp in the query matches the transmit time at one of the STAs,this STA sends a response message to node A. The response message mayinclude a TPC element providing link margin information to node A. Basedon the link margin, node A may then determine a suitable power level toensure deferral at node B and that a CTS sent by node A is received atnode B. Suitable transmit power may also computed by sending a sequenceof RTSs and increasing power levels until a CTS is received from a STA,such as node B, as described above.

FIG. 12 illustrates example operations 1200 to learn, from theperspective of a wireless node, for example, the transmit power used byan unknown neighboring node, in accordance with certain aspects of thepresent disclosure. The operations 1200 may begin, at 1202, byreceiving, at a first apparatus from a second apparatus, a packet thatcannot be decoded by the first apparatus. At 1204, the first apparatusmay determine at least one of a time or a duration corresponding to thepacket. The first apparatus may transmit a query with an indication ofthe at least one of the time or the duration at 1206. For certainaspects, the query may be transmitted via one or more channels in theTVWS. At 1208, the first apparatus may receive a message from the secondapparatus in response to the query, the message identifying the secondapparatus as a source of the packet. For certain aspects, the messageindicates a power used by the second apparatus to transmit the message.

According to certain aspects, the first apparatus may transmit asequence of request-to-send (RTS) messages at different transmit powerlevels to the second apparatus. The first apparatus may determine if aclear-to-send (CTS) message was received in response to at least one ofthe RTS messages corresponding to a particular one of the transmit powerlevels. For certain aspects, the transmit power levels may be increasingin the sequence of RTS messages. The particular one of the transmitpower levels may comprise a minimum transmit power level fortransmitting one of the RTS messages to the second apparatus and forreceiving the CTS message in response. The first apparatus may transmitat least one of data, a subsequent RTS message, or a subsequent CTSmessage to the second apparatus based on the particular one of thetransmit power levels.

For certain aspects, the first apparatus may transmit a request to thesecond apparatus and may receive a response from the second apparatusindicating a link margin based on the request. The first apparatus maytransmit data to the second apparatus based on the link margin.

FIG. 13 illustrates example operations 1300 to provide, from theperspective of a wireless node unknown to a neighboring node, forexample, the transmit power used by the wireless node, in accordancewith certain aspects of the present disclosure. The operations 1300 maybegin, at 1302, with the first apparatus transmitting a packet at aparticular time with a certain duration. At 1304, the first apparatusmay store at least one of the time or the duration for the packet. Thefirst apparatus may receive from a second apparatus a (broadcast) querywith an indication of at least one of a query time or a query durationfor the packet at 1306. For certain aspects, the first apparatus mayreceive the query via one or more channels in the TVWS. At 1308, thefirst apparatus may determine that the at least one of the query time orthe query duration substantially matches the at least one of the storedtime or the stored duration. At 1310, the first apparatus may transmit amessage to the second apparatus in response to the query, the messageidentifying the first apparatus as a source of the packet. For certainaspects, the message may indicate a power used by the first apparatus totransmit the message.

According to certain aspects, the first apparatus may receive arequest-to-send (RTS) message from the second apparatus. The firstapparatus may transmit a clear-to-send (CTS) message in response to theRTS message.

For certain aspects, the first apparatus may receive a request from thesecond apparatus. The first apparatus transmit a response to the secondapparatus indicating a link margin based on the request. The request maycomprise a transmit power control (TPC) request, and the response maycomprise a TPC response.

As described above, using a high transmit power causes CSMA deferralover a larger area due to the lower path loss in the TVWS band. Deferralover large areas limits spatial re-use. Therefore, one object of aspectsof the present disclosure is to increase spatial re-use of TVWSchannels. This may be accomplished by an intelligent reduction oftransmit power of RTS, CTS, and data. Naïve reduction of transmit poweris not sufficient because if the transmit power is too low, thereceiving STA may likely see interference from a large number of “hiddennodes,” thus preventing reception. However, high transmit powers may be“overkill” in many scenarios, leading to wasted battery power, forexample.

Accordingly, what is needed are techniques and apparatus to adjust datatransmit power to ensure reception at the intended PHY rate at thereceiver and to adjust CTS power to cause deferral only at selectedinterferers. Ideally, implementations would involve only minimal changesto the IEEE 802.11 standard.

Transmit power adaptation may be accomplished for the RTS, the CTS,and/or data. Transmit power determination for the RTS/data may involve amethod for a receiver-side (Rx-side) device to determine and convey atransmitter-side (Tx-side) transmit power. This transmit powerdetermination may use request response messages similar to current TPCmessages, described below. Transmit power determination for CTS mayentail a method to calculate the CTS transmit power sufficient to blockout dominant interferers. Beacons and RTSs may be augmented with datatransmit power information as described below. Transmit powerdetermination for CTS may involve a method for a STA to identifyinterferers to quiet with the CTS and send CTS with sufficient transmitpower to reach those interferers.

A TPC request/response mechanism has been defined in IEEE 802.11. Thismechanism allows transmitter/receiver pairs to determine a suitabletransmit power.

FIG. 14A illustrates a TPC request element 1400 and a TPC report element600, in accordance with certain aspects of the present disclosure. TheTPC request element 1400 may comprise an element ID field 1402 and alength field 1404. Each of these fields 1402, 1404 may have a length ofone octet (eight bits).

For RTS or data transmit power determination, the Tx-side device maysend a TPC request message to the Rx-side device. The Rx-side device mayrespond with a TPC report message that contains a link margin field 608.The link margin may be measured during the reception of thecorresponding TPC request. The transmit power field 606 may indicate atransmit power of the TPC report message. The Tx-side device maydetermine the indicated transmit power from the link margin indicated inthe TPC report message.

FIG. 14B illustrates a TPC request element 1450 with a modulation andcoding scheme (MCS) field 1452 and a TPC report element 600, inaccordance with certain aspects of the present disclosure. In order toenable the Tx-side device to request the power level desired forreception at a given MCS from an Rx-side device, the Rx-side deviceshould be able to provide a transmit power that is based on the pathloss to the Tx-side device and potential interference at the Rx-sidedevice. To accomplish this, the Tx-side device may send a requestmessage with the desired transmit MCS. The Rx-side device may compute apower margin M₁ that may most likely be applied to the transmit power ofthe request message to support the requested MCS based on the receivedpower (e.g., the RSSI, or received signal strength indicator) of therequest message. The Rx-side device may adjust (e.g., reduce) thecomputed power margin M₁ in the above step by a further factor (e.g., afactor of tolerable interference) to obtain the feedback link margin M₂.Any suitable method of determining the tolerable interference factor maybe employed. The Rx-side device may then send a message with the marginM₂ to the Tx-side device. The Tx-side device may apply the fed-backmargin M₂ to the transmit power used for the request message todetermine the power to be used for data transmissions at the requestedMCS.

For certain aspects, the Tx-side device may send a TPC request element1450 with the MCS field 1452. The Rx-side device may respond with a TPCreport element 600 with the link margin field 608 set according to theMCS, a path loss between the Rx-side device and the Tx-side device, anda desired signal-to-interference-plus-noise ratio (SINR) at the Rx side.Then, the Tx-side device may use the minimum transmit power indicatedfor the requested MCS based on the link margin returned.

FIG. 15 illustrates example operations 1500 to utilize, from theperspective of a Tx-side device, for example, a TPC request message witha desired MCS, in accordance with certain aspects of the presentdisclosure. The operations 1500 may begin, at 1502, with the Tx-sidedevice determining a MCS for transmitting data frames. At 1504, theTx-side device may transmit a TPC request message comprising anindication of the MCS. The Tx-side device may transmit the TPC requestmessage via one or more channels in a TVWS. For certain aspects, theindication of the MCS may comprise an IE in the request message. TheTx-side device may receive a TPC response message comprising anindication of a link margin, wherein the link margin is based on the MCSat 1506. At 1508, the Tx-side device may transmit data using the MCS anda transmit power based on the link margin.

FIG. 16 illustrates example operations 1600 to utilize, from theperspective of a Rx-side device, for example, a TPC request message witha desired MCS, in accordance with certain aspects of the presentdisclosure. The operations 1600 may begin, at 1602, with the Rx-sidedevice receiving a TPC request message comprising an indication of a MCSfor transmitting data frames to be received. For certain aspects, theindication of the MCS may comprise an IE in the request message. At1604, the Rx-side device may determine a link margin based on the MCS.The Rx-side device may transmit a TPC response message with anindication of the link margin at 1606. The Rx-side device may transmitthe TPC response message via one or more channels in a TVWS.

According to certain aspects, the Rx-side device may determine asignal-to-interference-plus-noise ratio (SINR) and a path loss, whereinthe link margin is based on the MCS, the SINR, and the path loss. TheRx-side device may determine a received power associated with therequest message, determine a power margin based on the received powerassociated with the request message, and adjust the power margin by afactor to obtain the link margin. For certain aspects, the factor may bea tolerable interference factor.

FIG. 17 illustrates an example station (STA) 1700 surrounded byinterfering STAs 1710, in accordance with certain aspects of the presentdisclosure. The CTS range 1702 of the STA 1700 is chosen according to APtransmit power and desired interference level.

In determining a transmit power for CTS messages, the Rx-side device(e.g., the STA 1700) may observe RTSs and beacons from neighboringinterferers (e.g., interfering STAs 1710). Beacons of neighboring APscontain the maximum transmit power used by the AP to transmit data. Forcertain aspects, the beacons may contain the transmit power of thebeacon, as well. Details for the beacon frame format are described belowwith respect to FIG. 18. Some RTSs transmitted from a STA are augmentedwith power used for the following data and the power used fortransmitting the RTS. Details on augmented RTS frame format are providedbelow with respect to FIG. 21.

The Rx-side device may use data transmit power information along withpath loss (determined from RSSI of the Beacon/RTS) to determine dominantinterferers. The Rx-side device may send a CTS message at a power levelsufficient to reach all the device's dominant interferers determinedbased on the data transmit power. Transmit power used for the beacon oraugmented RTS may be larger in order to ensure decode at a longer range.Using the beacon transmit power may lead to an unnecessarily large rangefor the CTS.

FIG. 18 illustrates an example beacon information element (IE) 1800 forindicating the transmit power of data frames transmitted from an accesspoint (AP), in accordance with certain aspects of the presentdisclosure. An AP may transmit beacons with the beacon IE 1800. Thebeacon IE 1800 may comprise an element ID field 1802, a length field1804, and a data transmit power field 1806. The data transmit powerfield 1806 may contain the highest transmit power used by the AP to senddata frames. Each of the fields 1802, 1804, 1806 may have a length ofone octet (8 bits).

FIG. 19 illustrates example operations 1900 to transmit, from theperspective of an AP, for example, a broadcast message with anindication of the highest transmit power for transmitting data frames,in accordance with certain aspects of the present disclosure. Theoperations 1900 may begin, at 1902, with the AP determining a highesttransmit power for transmitting data frames. At 1904, the AP maytransmit a (broadcast) message with an indication of the highesttransmit power. The AP may transmit the message via one or more channelsin a TVWS.

According to certain aspects, the message may comprise a beacon. Theindication may comprise an IE in the beacon. For other aspects, themessage may comprise another indication of a second transmit power fortransmitting the message. The AP may transmit the message using thesecond transmit power.

FIG. 20 illustrates example operations 2000 to determine, from theperspective of a STA, for example, dominant interferers based on areceived broadcast message with an indication of a highest transmitpower for transmitting data frames, in accordance with certain aspectsof the present disclosure. The operations 2000 may begin, at 2002, withthe STA receiving, from an apparatus (e.g., an AP), a (broadcast)message with an indication of a highest transmit power used by theapparatus for transmitting data frames. For certain aspects, the messagecomprises a beacon, and the indication comprises an IE in the beacon. At2004, the STA may determine that the apparatus is a dominant interfererbased, at least in part, on the highest transmit power. For certainaspects, this determination may also be based on the path loss. At 2006,the STA may determine a received power of the message. The STA maydetermine a path loss based on the received power at 2008. At 2010, theSTA may transmit a CTS message at a transmit power level sufficient toreach the dominant interferer.

According to certain aspects, the message may comprise anotherindication of a second transmit power for transmitting the message. TheSTA may determine a received power of the message and a path loss basedon the received power and the second transmit power. The STA maydetermine that the dominant is a dominant interferer is also based onthe path loss.

For certain aspects, the STA may receive from multiple apparatuses(e.g., a second or a third apparatus), messages with indications of thehighest transmit power used by each of the apparatuses for transmittingdata frames. For example, the STA may receive from a second apparatusanother message with another indication of a highest transmit power usedby the second apparatus for transmitting data frames. The STA maydetermine that any one or more of these apparatuses are dominantinterferers based, at least in part, on the highest transmit power usedby each of the apparatuses. The STA may then transmit a CTS message atthe highest transmit power level sufficient to reach all of the dominantinterferers (i.e., at the higher of a first transmit power levelsufficient to reach the apparatus and a second transmit power levelsufficient to reach the second apparatus).

FIG. 21 illustrates an example control or management frame format 2100with an IE for indicating the transmit power of data frames transmittedfrom a STA and another IE for indicating the transmit power used fortransmitting the control or management frame, in accordance with certainaspects of the present disclosure. The frame format 2100 may comprise aframe control (FC) field 2102, a duration field 2104, a receiver address(RA) field 2106, a transmitter address (TA) field 2108, a frame transmitpower field 2110, a data transmit power field 2112, and a frame checksequence (FCS) field 2114. The data transmit power field 2112 mayindicate the transmit power for transmitting data frames, while theframe transmit power field 2110 may indicate the power used fortransmitting the control or management frame containing the frametransmit power field 2110.

For certain aspects, the control or management frame may be a powercalibration frame, which may be a type of management frame. For otheraspects, the control or management frame format 2100 may be an RTS frameformat augmented with the frame and data transmit power fields 2110,2112.

FIG. 22 illustrates example operations 2200 to transmit, from theperspective of a STA, for example, a control or management message withan indication of a transmit power for transmitting data frames andanother indication of a transmit power used when transmitting thecontrol or management message, in accordance with certain aspects of thepresent disclosure. The operations 2200 may begin, at 2202, with the STAdetermining a first transmit power for transmitting data frames. At2204, the STA may transmit a control or management message at a secondtransmit power. The control or management message may comprise a firstindication of the first transmit power and a second indication of thesecond transmit power. The STA may transmit the control or managementmessage via one or more channels in a TVWS.

For certain aspects, the control or management message may comprise aRTS message or a power calibration frame. According to certain aspects,the first and second indications may comprise an IE in the control ormanagement message.

FIG. 23 illustrates example operations 2300 to determine, from theperspective of a STA, for example, dominant interferers based on areceived control or management message with an indication of a transmitpower for transmitting data frames and another indication of a transmitpower used when transmitting the control or management message, inaccordance with certain aspects of the present disclosure. Theoperations 2300 may begin, at 2302, with the STA receiving from anapparatus (e.g., another STA), a control or management message with afirst indication of a first transmit power used by the apparatus fortransmitting data frames. The STA may receive the control or managementmessage via one or more channels in a TVWS. For certain aspects, thecontrol or management message may also comprise a second indication of asecond transmit power used by the apparatus for transmitting the controlor management message. At 2304, the STA may determine that the apparatusis a dominant interferer based, at least in part, on the first transmitpower.

At 2306, the STA may determine a received power of the control ormanagement message. The STA may determine a path loss based on thereceived power and the second transmit power at 2308. For certainaspects, the STA may determine that the apparatus is a dominantinterferer at 2304 based on the path loss, as well as the first transmitpower. At 2310, the STA may transmit a CTS message at a transmit powerlevel sufficient to reach the dominant interferer.

For certain aspects, the control or management message may comprise aRTS message or a power calibration frame. According to certain aspects,one of the first and second indications may comprise an IE in thecontrol or management message.

For certain aspects, the STA may receive, from a second apparatus,another control or management message with a third indication of a thirdtransmit power used by the second apparatus for transmitting dataframes. The STA may determine that the second apparatus is anotherdominant interferer based, at least in part, on the third transmitpower. The STA may also transmit a CTS message at the higher of a firsttransmit power level sufficient to reach the apparatus and a secondtransmit power level sufficient to reach the second apparatus.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 700 illustrated in FIG. 7correspond to components 700A illustrated in FIG. 7A.

For example, means for transmitting may comprise a transmitter, such asthe transmitter unit 222 of the access point 110 illustrated in FIG. 2,the transmitter unit 254 of the user terminal 120 depicted in FIG. 2, orthe transmitter 310 of the wireless device 302 shown in FIG. 3. Meansfor receiving may comprise a receiver, such as the receiver unit 222 ofthe access point 110 illustrated in FIG. 2, the receiver unit 254 of theuser terminal 120 depicted in FIG. 2, or the receiver 312 of thewireless device 302 shown in FIG. 3. Means for processing, means fordetermining, means for identifying, or means for adjusting may comprisea processing system, which may include one or more processors, such asthe RX data processor 270, the TX data processor 288, and/or thecontroller 280 of the user terminal 120 or the RX data processor 242,the TX data processor 210, and/or the controller 230 of the access point110 illustrated in FIG. 2. Means for storing may comprise memory orother storage media, such as the memory 306 of the wireless device 302shown in FIG. 3.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the PHY layer. In the case of a user terminal 120 (see FIG. 1), auser interface (e.g., keypad, display, mouse, joystick, etc.) may alsobe connected to the bus. The bus may also link various other circuitssuch as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor may be responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media. The processor may be implemented with one ormore general-purpose and/or special-purpose processors. Examples includemicroprocessors, microcontrollers, DSP processors, and other circuitrythat can execute software. Software shall be construed broadly to meaninstructions, data, or any combination thereof, whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials.

In a hardware implementation, the machine-readable media may be part ofthe processing system separate from the processor. However, as thoseskilled in the art will readily appreciate, the machine-readable media,or any portion thereof, may be external to the processing system. By wayof example, the machine-readable media may include a transmission line,a carrier wave modulated by data, and/or a computer product separatefrom the wireless node, all which may be accessed by the processorthrough the bus interface. Alternatively, or in addition, themachine-readable media, or any portion thereof, may be integrated intothe processor, such as the case may be with cache and/or generalregister files.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC (Application SpecificIntegrated Circuit) with the processor, the bus interface, the userinterface in the case of an access terminal), supporting circuitry, andat least a portion of the machine-readable media integrated into asingle chip, or with one or more FPGAs (Field Programmable Gate Arrays),PLDs (Programmable Logic Devices), controllers, state machines, gatedlogic, discrete hardware components, or any other suitable circuitry, orany combination of circuits that can perform the various functionalitydescribed throughout this disclosure. Those skilled in the art willrecognize how best to implement the described functionality for theprocessing system depending on the particular application and theoverall design constraints imposed on the overall system.

The machine-readable media may comprise a number of software modules.The software modules include instructions that, when executed by theprocessor, cause the processing system to perform various functions. Thesoftware modules may include a transmission module and a receivingmodule. Each software module may reside in a single storage device or bedistributed across multiple storage devices. By way of example, asoftware module may be loaded into RAM from a hard drive when atriggering event occurs. During execution of the software module, theprocessor may load some of the instructions into cache to increaseaccess speed. One or more cache lines may then be loaded into a generalregister file for execution by the processor. When referring to thefunctionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media include both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage medium may be any available medium that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared (IR), radio, and microwave, then the coaxial cable,fiber optic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, include compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray®disc where disks usually reproduce data magnetically, while discsreproduce data optically with lasers. Thus, in some aspectscomputer-readable media may comprise non-transitory computer-readablemedia (e.g., tangible media). In addition, for other aspectscomputer-readable media may comprise transitory computer-readable media(e.g., a signal). Combinations of the above should also be includedwithin the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1-17. (canceled)
 18. A first apparatus for wireless communications,comprising: a receiver configured to receive from a second apparatus apacket that cannot be decoded by the first apparatus; a processingsystem configured to determine at least one of a time or a durationcorresponding to the packet; and a transmitter configured to transmit aquery with an indication of the at least one of the time or theduration, wherein the receiver is configured to receive a message fromthe second apparatus in response to the query, the message identifyingthe second apparatus as a source of the packet.
 19. The first apparatusof claim 18, wherein the transmitter is configured to transmit asequence of request-to-send (RTS) messages at different transmit powerlevels to the second apparatus and wherein the processing system isconfigured to determine if a clear-to-send (CTS) message was received inresponse to at least one of the RTS messages corresponding to aparticular one of the transmit power levels.
 20. The first apparatus ofclaim 19, wherein the transmit power levels are increasing in thesequence of RTS messages.
 21. The first apparatus of claim 19, whereinthe particular one of the transmit power levels comprises a minimumtransmit power level for transmitting one of the RTS messages to thesecond apparatus and receiving the CTS message in response.
 22. Thefirst apparatus of claim 19, wherein the transmitter is configured totransmit at least one of data, a subsequent RTS message, or a subsequentCTS message to the second apparatus based on the particular one of thetransmit power levels.
 23. The first apparatus of claim 18, wherein thetransmitter is configured to transmit the query via one or more channelsin a television white space (TVWS).
 24. The first apparatus of claim 18,wherein the transmitter is configured to transmit to the secondapparatus a request and wherein the receiver is configured to receive aresponse from the second apparatus indicating a link margin based on therequest.
 25. The first apparatus of claim 24, wherein the transmitter isconfigured to transmit data to the second apparatus based on the linkmargin.
 26. The first apparatus of claim 18, wherein the messageindicates a power used by the second apparatus to transmit the message.27. A method for wireless communications, comprising: at a firstapparatus, receiving from a second apparatus a packet that cannot bedecoded by the first apparatus; determining at least one of a time or aduration corresponding to the packet; transmitting a query with anindication of the at least one of the time or the duration; andreceiving a message from the second apparatus in response to the query,the message identifying the second apparatus as a source of the packet.28. The method of claim 27, further comprising determining if aclear-to-send (CTS) message was received, wherein the transmittingcomprises transmitting a sequence of request-to-send (RTS) messages atdifferent transmit power levels to the second apparatus and whereindetermining if the CTS message was received comprises determining if theCTS message was received in response to at least one of the RTS messagescorresponding to a particular one of the transmit power levels.
 29. Themethod of claim 28, wherein the transmit power levels are increasing inthe sequence of RTS messages.
 30. The method of claim 28, wherein theparticular one of the transmit power levels comprises a minimum transmitpower level for transmitting one of the RTS messages to the secondapparatus and receiving the CTS message in response.
 31. The method ofclaim 28, further comprising transmitting at least one of data, asubsequent RTS message, or a subsequent CTS message to the secondapparatus based on the particular one of the transmit power levels. 32.The method of claim 27, wherein transmitting the query comprisestransmitting the query via one or more channels in a television whitespace (TVWS).
 33. The method of claim 27, further comprising:transmitting to the second apparatus a request; and receiving a responsefrom the second apparatus indicating a link margin based on the request.34. The method of claim 33, further comprising transmitting data to thesecond apparatus based on the link margin.
 35. The method of claim 33,wherein the message indicates a power used by the second apparatus totransmit the message.
 36. A first apparatus for wireless communications,comprising: means for receiving from a second apparatus a packet thatcannot be decoded by the first apparatus; means for determining at leastone of a time or a duration corresponding to the packet; and means fortransmitting a query with an indication of the at least one of the timeor the duration, wherein the means for receiving is configured toreceive a message from the second apparatus in response to the query,the message identifying the second apparatus as a source of the packet.37. A computer-program product for wireless communications, comprising acomputer-readable medium comprising instructions executable to: receive,at a first apparatus from a second apparatus, a packet that cannot bedecoded by the first apparatus; determine at least one of a time or aduration corresponding to the packet; transmit a query with anindication of the at least one of the time or the duration; and receivea message from the second apparatus in response to the query, themessage identifying the second apparatus as a source of the packet. 38.A wireless node, comprising: at least one antenna; a receiver configuredto receive, from an apparatus via the at least one antenna, a packetthat cannot be decoded by the wireless node; a processing systemconfigured to determine at least one of a time or a durationcorresponding to the packet; and a transmitter configured to transmit,via the at least one antenna, a query with an indication of the at leastone of the time or the duration, wherein the receiver is configured toreceive a message from the apparatus in response to the query, themessage identifying the apparatus as a source of the packet.
 39. A firstapparatus for wireless communications, comprising: a transmitterconfigured to transmit a packet at a particular time with a certainduration; a receiver configured to receive from a second apparatus aquery with an indication of at least one of a query time or a queryduration for the packet; and a processing system configured to: store atleast one of the particular time or the certain duration for the packet;and determine that the at least one of the query time or the queryduration substantially matches the at least one of the stored time orthe stored duration, wherein the transmitter is configured to transmit amessage to the second apparatus in response to the query, the messageidentifying the first apparatus as a source of the packet.
 40. The firstapparatus of claim 39, wherein the receiver is configured to receive arequest-to-send (RTS) message from the second apparatus and wherein thetransmitter is configured to transmit a clear-to-send (CTS) message inresponse to the RTS message.
 41. The first apparatus of claim 39,wherein the receiver is configured to receive the query via one or morechannels in a television white space (TVWS).
 42. The first apparatus ofclaim 39, wherein the receiver is configured to receive from the secondapparatus a request and wherein the transmitter is configured totransmit a response to the second apparatus indicating a link marginbased on the request.
 43. The first apparatus of claim 42, wherein therequest comprises a transmit power control (TPC) request and wherein theresponse comprises a TPC response.
 44. The first apparatus of claim 39,wherein the message indicates a power used by the first apparatus totransmit the message.
 45. A method for wireless communications,comprising: at a first apparatus, transmitting a packet at a particulartime with a certain duration; storing at least one of the particulartime or the certain duration for the packet; receiving from a secondapparatus a query with an indication of at least one of a query time ora query duration for the packet; determining that the at least one ofthe query time or the query duration substantially matches the at leastone of the stored time or the stored duration; and transmitting amessage to the second apparatus in response to the query, the messageidentifying the first apparatus as a source of the packet.
 46. Themethod of claim 45, further comprising: receiving a request-to-send(RTS) message from the second apparatus; and transmitting aclear-to-send (CTS) message in response to the RTS message.
 47. Themethod of claim 45, wherein receiving the query comprises receiving thequery via one or more channels in a television white space (TVWS). 48.The method of claim 45, further comprising: receiving from the secondapparatus a request; and transmitting a response to the second apparatusindicating a link margin based on the request.
 49. The method of claim48, wherein the request comprises a transmit power control (TPC) requestand wherein the response comprises a TPC response.
 50. The method ofclaim 45, wherein the message indicates a power used by the firstapparatus to transmit the message.
 51. A first apparatus for wirelesscommunications, comprising: means for transmitting a packet at aparticular time with a certain duration; means for storing at least oneof the particular time or the certain duration for the packet; means forreceiving from a second apparatus a query with an indication of at leastone of a query time or a query duration for the packet; and means fordetermining that the at least one of the query time or the queryduration substantially matches the at least one of the stored time orthe stored duration, wherein the means for transmitting is configured totransmit a message to the second apparatus in response to the query, themessage identifying the first apparatus as a source of the packet.
 52. Acomputer-program product for wireless communications, comprising acomputer-readable medium comprising instructions executable to: transmitfrom a first apparatus a packet at a particular time with a certainduration; store at least one of the particular time or the certainduration for the packet; receive from a second apparatus a query with anindication of at least one of a query time or a query duration for thepacket; determine that the at least one of the query time or the queryduration substantially matches the at least one of the stored time orthe stored duration; and transmit a message to the second apparatus inresponse to the query, the message identifying the first apparatus as asource of the packet.
 53. A wireless node, comprising: at least oneantenna; a transmitter configured to transmit, via the at least oneantenna, a packet at a particular time with a certain duration; areceiver configured to receive, from an apparatus via the at least oneantenna, a query with an indication of at least one of a query time or aquery duration for the packet; and a processing system configured to:store at least one of the particular time or the certain duration forthe packet; and determine that the at least one of the query time or thequery duration substantially matches the at least one of the stored timeor the stored duration, wherein the transmitter is configured totransmit a message to the apparatus in response to the query, themessage identifying the wireless node as a source of the packet.